1. The problem statement, all variables and given/known data Need to prove that: ,b means partial differentation with respect to b, G is the metric tensor and Γ is Christoffel symbol. I think I could proceed with this quite well if I could understand the hint given, that I should lower the index j. 2. Relevant equations am=Gmjaj 3. The attempt at a solution For the first member on the left I could write GmjGjk∂k=δkm∂k=∂k and else than that it should stay the same For members on the right, lowering j would give me vα(vj,α+Γjαβvβ) However, what should I do with the second member on the left? And I am told that this one is the important one.